Astroboffins suspect twin-star smash may be the culprit for most biggest and brightest supernova yet spotted

A rogue pulsational pair-instability nova from a heavy star measuring over 100 times the mass of the Sun

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Astronomers have spotted the biggest and brightest supernova explosion yet spotted and theorize it may have been sparked by two huge stars smashing together.

“In a typical supernova, the radiation is less than 1 per cent of the total energy," said Dr Matt Nicholl, of the School of Physics and Astronomy at the University of Birmingham,.

"But in SN2016aps, we found the radiation was five times the explosion energy of a normal-sized supernova. This is the most light we have ever seen emitted by a supernova.”

The gargantuan eruption was five times more energetic and 500 times more luminous than normal events, leading researchers to speculate that the object could be a “pulsational pair instability” supernova. These types of explosions are incredibly unusual; their existence has been predicted theoretically, but they have never been confirmed in observations before.

“SN2016aps is spectacular in several ways," said Edo Berger, co-author of the study published in Nature Astronomy on Monday and a professor of astronomy at Harvard University. "Not only is it brighter than any other supernova we’ve ever seen, but it has several properties and features that make it rare in comparison to other explosions of stars in the universe."

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The researchers monitored SN2016aps’ activity over two years until it’s glow petered out to one per cent of its peak brightness using NASA’s Hubble Space Telescope. They calculated that the total mass of the supernova is somewhere between 50 to 100 solar masses, far greater than the eight to 15 solar mass explosions typically observed.

"The intense energy output of this supernova pointed to an incredibly massive star progenitor," said Berger. "At birth, this star was at least 100 times the mass of our Sun." A hefty star of that size would undergo large pulsational pair-instability eruptions, where its core begins pulsing and pushing out material in a surrounding envelope before it collapses.

"We determined that in the final years before it exploded, the star shed a massive shell of gas as it violently pulsated,” said Matt Nicholl, lead author of the study and an assistant professor at the University of Birmingham. “The collision of the explosion debris with this massive shell led to the incredible brightness of the supernova. It essentially added fuel to the fire."

SN2016aps is also strange because it may have formed when two smaller stars merged. The researchers detected high levels of hydrogen, something that isn’t seen in normal supernova explosions since the gas is normally blown away in stellar winds.

"That SN2016aps held onto its hydrogen prompted us to theorize that two less massive stars had merged together, since lower mass stars hold onto their hydrogen for longer,” said Berger. "The new star, borne of the merger, was heavy with hydrogen and also high enough in mass to trigger pair instability."

Now, the team are working to confirm their idea by building detailed simulations of the outburst.

"While many supernovae are discovered every night, most are in massive galaxies," said Peter Blanchard, co-author of the paper and a postdoctoral fellow at Northwestern University.

"This one immediately stood out for further observations because it seemed to be in the middle of nowhere. We weren't able to see the galaxy where this star was born until after the supernova light had faded." ®

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